Coated abrasive containing an over-size layer of a metal halide



United States Patent 01 3,541,739 Patented Nov. 24, 1970 3,541,739 COATED ABRASIVE CONTAINING AN OVER-SIZE LAYER OF A METAL HALIDE John P. Bryon, Potters Bar, and Alan G. Rolfe, London,

England, assignors to English Abrasives Limited, London, England No Drawing. Filed July 16, 1968, Ser. No. 745,106 Int. Cl. B24d 11/00; C08g 57/12 US. Cl. 51-295 14 Claims ABSTRACT OF THE DISCLOSURE A coated abrasive article comprising a backing, abrasive particles, and a bond securing the particles to the backing, such abrasive being oversized With a top coating of a reactive filler above the conventional sand size coating normally applied in the industry, such filler consisting of or containing a simple or complex halide, the proportion of such filler being 4095% by weight of the total dry oversizing weight the remaining percentage being an adhesive to bind the filler to the abrasive surface.

This invention relates to flexible coated abrasive articles, more particularly it relates to coated abrasive articles which are suitable for dry grinding of metals.

The use of various additives has been suggested to improve the rate of cut of coated abrasives. When metal is ground, there is a tendency for glazing of the abrasive surface to occur and for particles of metal to become welded to the tops of the grains. The action of additives to the adhesive bond is to reduce this tendency to glaze and weld. In particular, compounds containing halogens and/ or sulfur have been suggested. Thiourea, mercaptans, thiuram tetrasulfide, 2:4 dichlorobenzoic acid, chlorinated alkyl esters of phosphoric acid are cited.

In the case of bonded abrasives such as grinding Wheels, similar additives have been suggested to aid cutting in certain cases, but in most instances, inorganic fillers have been employed. Sodium cryolite has been used for some time in bonded abrasive wheels and more recently such materials as potassium fluoroborate, alkali metal halides and iron sulfide have been used. In ljat. 3,246,970 to Zimmerman issued Apr. 19, 1966, for instance, claims have been made for the use of potassium cryolite and iron sulfide as a filler giving improved performance to a grinding Wheel. From the fact that such materials improve the performance of a grinding wheel, it can in no way be inferred that the inclusion of the same materials in a coated r abrasive product will result in a similar improvement in performance. Whereas, a grinding wheel has a multiplicity of grain layers and wears more or less rapidly in use, a coated abrasive has only a monolayer of grit, and the factor which determines its life is in many cases the degree of blunting of the grit and the capping of the grit with metal swarf particles, and not the degree of grit loss. This particularly applies when metals such as stainless steel and high temperature resistant nickel alloys are being ground.

It is well known that in the literature reference is made to the inclusion of metallic halides, sulfides and other fillers in coated abrasives and amongst these materials sodium cryolite is mentioned. The use of sodium cryolite and other metallic halides in practice however has not been widespread in the manufacture of coated abrasives. In the case of sodium cryolite, this has been used as a supposedly inert filler, as is evidenced by references to its use as an alternative to such fillers as walnut shell flour, calcium carbonate or silica. Such references are to be found in Pat. 3,232,729 to Holland et al. issued Feb. 1, 1966, Example 7; and in Pat. 2,468,056 to Goepfert et al. issued Apr. 26, 1949 Examples II and III. The reason and that materials such as sodium cryolite have been deemed inert is that they have often been present in quantities too small to exert an influence on the grinding mechanism, or else have been included in the making or first layer of adhesive where they can make little or no contribution to the cutting process as they are covered with the sandsize or top coat of adhesive. (See Pat. 2,468,056 Example H). When the halide or sulfide fillers are included in the sand-size coat, a limit is imposed on the amount that can be included, by the reduction in strength of the adhesive which results at high level of addition. In practice, therefore, no great increase in performance can be expected from the inclusion in coated abrasive of many of the fillers and additives which give good results in wheels.

The present invention relates to a method whereby the tendency for coated abrasives to blunt and become covered with metal during grinding is considerably reduced whilst the rate of cut of the abrasive increases to a remarkable degree. This improvement is achieved by applying to the surface of a conventional coated abrasive above the grit and sand-size an oversize layer containing certain reactive fillers. These fillers consist mainly of simple or complex metallic halides, but other materials such as iron pyrites, zinc sulfide or emery powder may also be present. The proportion of filler in the bond is to be from to 95% by weight of the total dry weight of the layer, the remainder of the layer consisting of a binder to hold the reactive fillers to the abrasive surface. The binder may be one of a number of adhesives such as are well known in the abrasives industry such as animal glue, phenolic resins, urea formaldehyde resins or alkyd resins. With the limits of filler content of 40-95% stated above, proportions of are to be preferred.

Alkali metal halides particularly effective are sodium or potassium chloride and sodium or potassium bromide. When the halides are used alone, the greatest improvement in the rate of cut of the abrasive is obtained with sodium or potassium bromide. When used in conjunction with sodium or potassium aluminum hexafluoride, the results obtained are surprisingly greater than those obtained with either of the constituents alone.

Potassium borofluoride and sodium silicofiuoride among other complex halides have been shown to give results similar to those obtained from potassium cryolite.

It has, moreover, been found as in the case of mixtures of simple and complex halides that mixtures of potassium fiuoroborate and potassium or sodium cryolite give results which excel those obtained by either component alone.

It has been found possible to blend the fillers of this invention with many additional fillers such as fine emery powder, slate, or metallic sulfides and similar results are obtained as when the reactive fillers of the invention are used alone.

It has been noticed that coated abrasive articles oversized with the reactive layer described in this application not only give better initial cut, but that their life is extended. Whereas such improvements are experienced in the case of mild steel and aluminum alloy grinding. The greatest improvement is experienced when grinding high temperature resistant nickel based alloy and also stainless steels, both of which metals are very difficult to grind with conventional coated abrasives.

In order to show the improvements in cutting performance obtainable with the coatings of this invention, the following oversizing formulations are given as examples.

The oversizing was applied in each case to a conventional coated abrasive which had been made as follows:

A heavy twill backing was coated with a resole phenolic making coat, modified with a dolomite filler, at the rate of 220 gms./square metre and Grade 60 aluminum oxide grain was applied at the rate of 470 gms./square metre. After partial cure of the making coat, a sand size coat a was applied at the rate of 200 gms./square metre, this sand-size coat being of similar composition to that of the making coat and the whole article was subject to heat cure as is normal in the industry, the resole phenolic resin referred to is a blend of two commercially available resinsBakelite NPA manufactured by BXL Plastics Ltd. and AC223 resin manufactured by Charles Lowe (Manchester) Ltd. The blend has a viscosity of about 30 poises and a gelation time at 130 C. of 6 /2 minutes.

EXAMPLE 1 A standard resin bonded aluminum oxide cloth grade 60 made as described above was coated with an even layer of an oversize coating consisting of 88% by weight of potassium bromide and 12% by weight of a resole phenolic resin, these weights being on a dry basis. The oversize coating was then cured by application of heat to bind the potassium bromide firmly to the surface of the abrasive, the resole phenolic resin referred to in this and subsequent examples is AC223 resin manufactured by Charles Lowe (Manchester) Ltd., having a viscosity of approximately 30 poises and a gelation time at 130 C. of approximately minutes.

A test was performed to assess the cutting ability of this material, in which a stainless steel test piece was loaded against an abrasive belt for five one-minute runs. The load applied was 5 /2 lbs. A belt was taken from the standard production material before oversizing with the potassium bromide coating.

The total metal removed in each case was:

Gms. Potassium bromide coated belt 51 Uncoated standard belt 30 It was found that not only was the initial cut better with the oversized belt, but the life of the belt was extended. Similar results were obtained with oversize coats of sodium bromide, sodium or potassium chloride and sodium or potassium iodide. The best results were obtained with the bromides, however.

EXAMPLE 2 A standard resin bond cloth grade 60 made as described above was oversized with a layer containing 88% by weight of sodium aluminum fluoride mixed with fine emery powder in 50:50 weight proportions and 12% by weight of a resole phenolic resin on a dry basis. The coating was cured as before.

Metal removal tests were carried out as described before, and the results were as follows:

Gms. Belt oversized with sodium aluminum fluoride/emery mixture 57 Uncoated standard belt 33 EXAMPLE 3 A standard resin bond cloth grade 60 made as described above was oversized with a layer containing 88% by weight of potassium aluminum fluoride mixed with fine emery powder in 50:50 weight proportions and 12% by weight of a resole phenolic resin on a dry basis. The coating was cured as before.

Metal removal tests were carried out as described before, and the results were as follows:

Gms.

Belt oversized with potassium aluminum fluoride/ emery mixture 78 Uncoated standard belt 33 EXAMPLE 4 A standard resin bond cloth grade 60 made as described above was oversized with a layer containing 88% by weight of potassium fluoroborate mixed with fine emery powder in 50:50 weight proportions and 12% by 4 weight of a resole phenolic resin on a dry basis. The coating was cured as before.

Metal removal tests were carried out as described before, and the results were as follows:

Gms.

Belt oversized with potassium fiuoroborate/emery mixture 67 Uncoated standard belt 31 EXAMPLE 5 A standard resin bond cloth grade 60 made as described above was oversized with a layer containing 88% by weight of potassium aluminum fluoride/ potassium fluoroborate mixture in 60:40 weight proportions and 12% by weight of a resole phenolic resin on a dry basis. The coating was cured as before.

Metal removal tests were carried out as described before, and the results were as follows:

Gms.

Belt oversized with potassium fiuoroborate/potassium aluminum fluoride mixture 82.5 Uncoated standard belt 31.0

Although a proportion by weight of 88% filler is stated throughout the above examples, this was fixed in order to make the results shown comparative, and this stated proportion of filler is not intended to be limiting in any way. As stated earlier 4095% of filler may be employed, although proportions in the range of 65-90% are preferred.

EXAMPLE 6 A standard resin bonded aluminum oxide cloth grade 60 made as described above was coated with an even layer of an oversize coating consisting of 88% by weight of a 50:50 mixture of potassium aluminum fluoride and finely divided iron sulfide and 12% by weight of a resole phenolic resin, these weights being on a dry basis. The oversize coating was then cured by application of heat to bind the potassium aluminum fluoride firmly to the surface of the abrasive.

A test was performed to assess the cutting ability of this material, in which a stainless steel test piece was loaded against an abrasion belt for five one-minute runs. The load applied was 5 /2 lbs. A belt was taken from the standard production material before oversizing with the potassium aluminum fluoride coating.

The total metal removed in each case was:

Gms. Belt oversized with Potassium cryolite/iron sulfide mixture 7O Uncoated standard belt 31 Although the examples given refer to cloth backed abrasives, fibre or paper backings may be employed and the product may be in the form of belts, discs or sheets.

We claim:

1. A coated abrasive article comprising a backing of sheet material, abrasive particles, a layer of adhesive material serving as a bond to secure said particles to said backing, a sand-size coating of adhesive material selected from the group consisting of animal glue, [phenolic resins, urea resins or epoxide resins,] proteins, cellulose derivatives, sodium silicate, and synthetic thermosetting and thermoplastic resins, and an additional over-size layer applied as a top coating over said sandsize coating, wherein said over-size layer contains fine particulate inorganic powder including a metal halide selected from simple alkali metal halides and complex metal halides derived from alkali metal halide wherein the element other than alkali metal and halogen is selected from aluminum, boron and silicon, the said metal halide being in a proportion of from 40% to by weight of the total dry oversizing composition, and an adhesive serving to bond the said powder to the surface of the said abrasive, the adhesive being selected from the aforesaid group of adhesive materials.

2. A coated abrasive article in accordance with claim 1, wherein said over-size coating is a mixture of said metal halide with a finely divided metallic sulfide of iron and zinc.

3. A coated abrasive article in accordance with claim 1, wherein said coating is a mixture of complex metal halides.

4. A coated abrasive article in accordance with claim 1, wherein said coating is a mixture of a simple and a complex metal halide.

5. A coated abrasive article in accordance with claim 1, wherein said metal halide is selected from the group of alkali metal halides consisting of sodium and potassium bromides.

6. A coated abrasive article in accordance with claim 1, wherein said metal halide is selected from the group of alkali metal halides consisting of sodium and potassium aluminum fluoride.

7. A coated abrasive article in accordance with claim 1, wherein said metal halide is potassium fluoroborate.

8. A coated abrasive article in accordance with claim 1, wherein said layer is a mixture of complex metal halides, said complex halides being sodium aluminum fluoride and potassium fluoroborate.

9. A coated abrasive article in accordance with claim 1, wherein said layer is a mixture of complex metal halides, said complex halides being potassium aluminum fluoride and potassium fluoroborate.

10. A coated abrasive article in accordance with claim 1, wherein said layer is a mixture of a simple and a complex metal halide, said halide being selected from the group of alkali metal halides consisting of sodium and potassium bromides and said complex halide being selected from the group of alkali metal halides consisting of sodium and potassium aluminum fluorides.

11. A coated abrasive article in accordance with claim 1, wherein said layer is a mixture of a simple and a complex metal halide, said simple halide being selected from the group of alkali metal halides consisting of sodium and potassium bromides and the complex halide is potassium fluoroborate.

12. A coated abrasive article in accordance with claim 1, wherein said layer in said over-size coating is a mixture of said metal halide with a finely divided metallic sulfide, said finely divided metallic sulfide being iron pyrites.

13. A coated abrasive article in accordance with claim 1, wherein said layer in said over-size coating is a mixture of said metal halide with a finely divided metallic sulfide, said finely divided metallic sulfide is zinc sulfide.

14. A coated abrasive article comprising a backing of sheet material, abrasive particles, a layer of adhesive material serving as a bond to secure said particles to said backing, a sand-size coating of adhesive material selected from the group consisting of animal glue, proteins, cellulose derivatives, sodium silicate, and synthetic thermosetting and thermoplastic resins, and applied as a top coating over said sand-size coating, a layer of fine particulate inorganic powders comprising essentially a metal halide selected from the group consisting of simple alkali metal halides and complex metal halides derived from alkali metal halides wherein the element other than alkali metal and halogen is selected from the group consisting of aluminum, boron and silicon, the said layer being bound to the said sand-size coating by an adhesive likewise selected from the said group of adhesive materials, the proportion of the said halide in the said layer being between and by weight of the layer.

References Cited UNITED STATES PATENTS 2,111,272 3/1938 Paulson 5l298.1 2,236,597 4/1941 Hatch 51-2981 2,536,871 1/1951 Carlton 51-298 3,058,819 10/1962 Paulson 51-295 3,246,970 4/ 1966 Zimmerman 51-298 3,256,076 6/ 1966 Duwell et al. 51-298 DONALD J. ARNOLD, Primary Examiner US. Cl. X.-R. 

